The increase of the demand for communications has widely defused optical networks using Wavelength Division Multiplexing (WDM) technology. The wavelength division multiplexing technology is technology that multiplexes and transmits optical signals of different wavelengths. The wavelength division multiplexing technology enables to multiplex and transmit 40 waves of optical signals with a transmission rate of 40 (Gbps) as a wavelength-multiplexed optical signal (hereinafter, described as a multiplexed optical signal) with a transmission rate of 1.6 (Tbps).
There has been known an optical add-drop multiplexer referred to as a ROADM (Reconfigurable Optical Add-Drop Multiplexer) or the like as a transmission device using the WDM technology. The optical add-drop multiplexer includes optical transceivers referred to as a transponder or the like. The optical transceivers transmit/receive optical signals of different wavelengths to/from an external network.
The optical add-drop multiplexer multiplexes optical signals of different wavelengths input from the optical transceivers and transmit them to another node as a multiplexed optical signal. Moreover, the optical add-drop multiplexer receives a multiplexed optical signal from another node, and demultiplexes the multiplexed optical signal into one or more optical signals of desired wavelengths and output them to one or more optical transceivers. The optical add-drop multiplexer adds and drops the optical signal of a desired wavelength by the above described process.
The optical add-drop multiplexer includes a Wavelength Selective Switch (WSS) in each network degree to multiplex optical signals into a multiplexed optical signal or to demultiplex a multiplexed optical signal into optical signals of respective wavelengths. Here, the network degree is a transmission route between the optical add-drop multiplexer and another node to be connected.
Regarding the optical add-drop multiplexer, Japanese Patent Application Publication No. 2012-23781 (Patent Document 1) discloses providing wavelength selective switches with different frequency intervals for wavelength selection to add and drop optical signals with different transmission rates. Japanese Patent Application Publication No. 2005-143036 (Patent Document 2) discloses multiplexing optical signals with wavelengths of which the channel numbers are even numbers and optical signals with wavelengths of which the channel numbers are odd numbers by different optical multiplexers and demultiplexing them by different optical demultiplexers.